Sharing web apps to allow users from other organizations to edit and modify files?

I'm currently working on a student project to use WebApp Builder to create a web app for an outside client. Ideally this application will be able to be hosted, maintained, and updated by the client after I've finished it and graduated. Currently the map is created under my student account with my school's organization, and I'm struggling with finding a way to easily share the web app, the original map, and all hosted layers with my client.

I looked into sharing with groups, but from my understanding, my client would be unable to download the files to host on their own account, and unable to make any updates. Is there any simple method to this, such as downloading all necessary files/apps and then uploading them to the client's account?